Parthenogenesis is defined as the reproduction of an organism in the absence of fertilization. Artificial activation of mouse oocytes is possible; however, parthenogenetic embryos more suitable for embryological studies, are obtaind from females of the LT inbred mouse strain in which approximately 10 percent of released oocytes are spontaneously activated. Although parthenogenetic mouse oocytes, either artificially or spontaneously activated, develop through the preimplantation embryonic stages and implant in the uterus, they die shortly thereafter. Birth of a mouse of other mammalian parthenote has not been substantiated. The objective of the proposed research is to determine the reason for the early death of LT parthenogenetic embryos. These studies may produce a better understanding of the interaction between the sperm and oocyte which results in zygote development and information as to the cause of embryonic mortality in mammals. Recently we achieved full-term development after inner cell mass cell nuclei of LT parthenogenetic blastocysts were transplanted into fertilized and enucleated mouse eggs. Four offspring were born whose development was exclusively from the transplanted nucleus. These preliminary results demonstrate that (a) the LT parthenogenetic nucleus will support viable development when transplanted into the cytoplasm of fertilized eggs, and suggests that (b) early parthenogenetic mortality may be due to cytoplasmic deficiencies. A specific aim of the present proposal is to examine this latter suggestion by observing the subsequent development of eggs derived by transplantation of nuclei from fertilized embryos into enucleated parthenogenetic eggs. In view of a possible cytoplasmic deficiency, we will attempt to "rescue" the development of parthenogenetic embryos by introducing sperm into the eggs' cytoplasm by microinjection or fusion. These studies should elucidate the stimulus, substance, or organelle contributed by the sperm to the egg at the time of fertilization which allows viable development of the mouse zygote.